GABA is an amino acid which is currently drawing attention since it has physiological effects such as a hypotensive effect, a diuretic effect and a tranquilizing effect. Since the food containing GABA is limited to some vegetable, tea, rice and the like and its content is also small, some methods for producing GABA using GABA fermenting lactic acid bacteria are proposed (e.g., see Patent References 1 to 3). As such GABA producing lactic acid bacteria, Lactobacillus hilgardii, Lactococcus lactis subspecies cremoris, Lactococcus lactis subspecies lactis, Enterococcus casseliflavus, Lactobacillus brevis, Lactobacillus plantarum, Streptococcus thermophilus and the like are known, which have the ability to produce GABA from L-glutamic acid or a salt of L-glutamic acid by decarboxylation reaction.
However, since these lactic acid bacteria require expensive components such as whey powder, skimmed milk, casein and peptone for the medium, the productivity from the viewpoint of cost is not good (e.g., see Patent Reference 1 or 4). Also, when soy sauce koji or gluten as an inexpensive material is degraded with an acid or degraded with an enzyme or koji, and the eluted glutamine is converted into glutamic acid by glutaminase to be used as the medium, the common salt generated by the neutralization or the common salt added as an antipollution countermeasure at the time of the enzymatic degradation inhibits the GABA production of lactic acid bacteria. Although several salinity tolerant GABA producing lactic acid bacteria have been reported, the optimum common salt concentration for GABA fermentation is a markedly high salinity of from 12.5 to 18% (e.g., see Patent Reference 5). When the promotion of a dietary life of intending hypochloric diet in order to avoid life style-related diseases is taken into consideration, the food and seasonings having high common salt content are not desirable. Additionally, since there is a side of expecting hypotensive activity from GABA, combination of it with high common salt concentration loses the original meaning.
Based on the above, for producing GABA by a lactic acid bacterium, although it is ideal to use inexpensive material such as koji and gluten by degrading it under a low common salt concentration, the low common salt concentration poses a problem of causing pollution by wild strains. The pollution occurs at an early stage of the culturing, and when an alcohol is produced or pH is lowered as a result, growth of the GABA producing lactic acid bacterium is inhibited. Therefore, sufficient amount of the object GABA cannot be obtained. As a means for preventing pollution by these wild strains at a low common salt concentration, there is a method which uses ethanol, acetic acid and lactic acid which are generally frequently used as food antiseptics. However, although ethanol and acetic acid suppress the contaminants, they also suppress the GABA producing lactic acid bacterium. On the other hand, since lactic acid bacteria produces lactic acid by themselves, they have higher resistance to lactic acid than other bacteria.
Accordingly, although the inventors of the present invention have considered about the use of lactic acid as antiseptics, there is a new problem that the GABA producing lactic acid bacterium cannot grow when lactic acid is added at the time of the commencement of culturing in the presence of common salt, or can grow but does not produce GABA.    Patent Reference 1: JP-A-2000-210075    Patent Reference 2: JP-A-2004-215529    Patent Reference 3: JP-A-2005-102559    Patent Reference 4: Japanese Patent No. 3426157    Patent Reference 5: Japanese Patent No. 2704493